Purified hydrogen gas is used in the manufacture of many products including metals, edible fats and oils, and semiconductors and microelectronics. Purified hydrogen gas is also an important fuel source for many energy conversion devices. For example, fuel cells use purified hydrogen gas and an oxidant to produce an electrical potential. Various processes and devices may be used to produce the hydrogen gas that is consumed by the fuel cells. One such process is steam reforming, in which hydrogen gas is produced as a majority reaction product from a carbon-containing feedstock and water.
Steam reforming of water and a carbon-containing feedstock to produce hydrogen gas is an endothermic reaction. Hydrogen-producing steam reforming reactions are typically performed at elevated temperatures and pressures, such as temperatures of at least 200° C., and more typically at least 350° C., and pressures of at least 50 psi. The desired steam reforming temperature, or range of temperatures, will tend to vary according to a variety of factors, including the composition of the carbon-containing feedstock. As an illustrative example, steam reforming of methanol to produce hydrogen gas is typically performed at a temperature of 350-450° C., while many hydrocarbons are reformed to produce hydrogen gas at a temperature of 700-850° C.
When a hydrogen-producing steam reformer is initially started up from an unheated, or off, operating state, at least the hydrogen-producing region of the steam reformer needs to be initially heated to at least a minimum hydrogen-producing temperature. Because the steam reforming reaction is endothermic, the hydrogen-producing region is often heated to above this minimum hydrogen-producing temperature before water and the carbon-containing feedstock are delivered thereto, typically in gaseous form, to produce hydrogen gas therefrom. A heating assembly is typically utilized to provide the required preheating of the hydrogen-producing region, with burners, resistive heaters, and combustion catalysts being the most common sources of the required heating. Burners and combustion catalysts require the delivery of a suitable combustible fuel stream, the presence or delivery of a sufficient air stream to support the combustion, and suitable controls and delivery conduits to safely and reliably deliver and combust the fuel stream and to deliver the heated exhaust stream produced thereby to heat at least the hydrogen-producing region of the steam reformer. Electrically powered heaters require a sufficient power source for the heaters to generate sufficient heat throughout the hydrogen-producing region.